534 THE NERVOUS SYSTEM 



THE MEDULLA OBLONGATA OR BULB. 



Anatomical Structure. The medulla oblongata is continuous with 

 the spinal cord at its upper end. It lies within the cranial cavity and forms 

 the first part of the brain stem. The medulla consists of masses of nerve 

 cells situated in the interior, but pretty generally distributed throughout 

 the mass. The cell- masses are subdivided by laminae of nsrve fibers into 

 groups, or nuclei, which give origin to or form the terminations of the various 

 ranks of nerve fibers. 



The nerve fibers are arranged partly in columns and partly in fasciculi 

 traversing the central cellular matter. The medulla oblongata is larger than 



FIG. 373. Plan in Outline of the Brain as seen from the Right Side. X. The parts are repre- 

 sented as separated from one another somewhat more than natural, so as to show their connections. 

 A, Cerebrum; /, g, h, its anterior, middle, and posterior lobes; e, fissure of Sylvius; B, cerebellum; 

 C, pons Varolii; D, medulla oblongata; a, peduncles of the cerebrum; b, c, d, superior, middle, 

 and inferior peduncles of the cerebellum. (From Quain.) 



any part of the spinal cord. Its columns are pyriform, enlarging as they pro- 

 ceed toward the brain, and are continuous with those of the spinal cord. Each 

 half of the medulla, therefore, may be divided into three columns or tracts of 

 fibers, continuous with the three columns of which each half of the spinal cord 

 is made up, but the columns are more prominent than those of the spinal cord, 

 and are separated from each other by deeper grooves. The anterior, contin- 

 uous with the anterior columns of the cord, are called the pyramids. The 

 postero-median and postero-external columns are also represented at the 

 posterior or dorsal aspect of the cord as the fasciculus gracilis and the fasciculus 

 cuneatus. The posterior pyramids of the medulla, which include these two 

 columns of white matter, soon become much increased in width by the addi- 

 tion of a new column of white matter outside the other two, which is known 



